The present invention relates to a lenticular lens sheet for use in a rear projection screen. More particularly, it relates to a lenticular lens sheet including on its light-emerging surface side a light-shielding layer, and to a process of producing the same.
A so-called projection-type television, which an image is projected from the rear and the projected image is viewed from the front, is known as a large-screen television. Such a projection-type television includes an imaging light source and a rear projection screen for displaying thereon an image projected from the imaging light source. Currently used for the imaging light source are CRT""s (cathode-ray tubes) for projection, characterized by higher luminance than that of ordinary CRT""s, as well as liquid crystal display (LCD) projectors, digital light processing (DLP) projectors using digital micro-mirror devices (DMD""s), and the like.
FIG. 7 is a view showing an example of a rear projection screen for use in a projection-type television. As shown in this figure, a rear projection screen 10 is composed of a Fresnel lens sheet (Fresnel convex lens) 11 and a lenticular lens sheet 12, where an image projected from an imaging light source (not shown in the figure) located at the rear of the rear projection screen 10 (upside in the figure) is viewed by a viewer who is in front of the rear projection screen 10 (downside in the figure). In the rear projection screen 10 shown in FIG. 7, when light 20 emitted by the imaging light source (not shown in the figure) located at the rear of the rear projection screen 10 (upside in the figure), the rays of the light 20 spreading to a certain extent, enters the rear projection screen 10, this incident light 20 is converged by the Fresnel lens sheet 11 to become, for example, parallel rays 21. These parallel rays 21 are converged by lenticular lenses 13 that are provided on the lenticular lens sheet 12 on its light-entering surface side, and go out as emergent light 22 from the light-emerging surface side of the lenticular lens sheet 12 at an angle in the range xcex8. This angle range xcex8 is the range in which the projected image is visible.
As shown in FIG. 7, the lenticular lens sheet 12 for use in such a rear projection screen 10 contains, on its light-emerging surface side, a light-shielding layer 14 in order to prevent reflection of extraneous light (light that enters from the downside in FIG. 7) to improve image contrast. The light-shielding layer 14 has light-shielding areas (black stripes) 14a that correspond to the non-light-converging parts of the lenticular lenses 13. The light-shielding areas 14a in the light-shielding layer 14 can be created by coating, with a material capable of shielding light, those parts with a certain width of the light-emerging surface of the lenticular lens sheet 12 that correspond to the non-light-converging parts of the lenticular lenses 13.
It is necessary to create the light-shielding areas 14a in the light-shielding layer 14 as large as possible in such positions that the incident light 20 projected from the rear does not go out, with high positional accuracy relative to the lenticular lenses 13 having the function of converging the incident light 20. There is therefore a heavy demand for a method of accurately creating the light-shielding areas 14a in the light-shielding layer 14.
In recent years, an LCD or DLP projector, or the like has come to be used, instead of a CRT, in a projection-type television as an imaging light source. An image projected from such a light source is composed of dot matrixes and has sharper definition. For this reason, a so-called fine-pitch lenticular lens sheet 12 with a lens pitch smaller than that required for the magnifying projection of an image on a CRT has come to be demanded. Specifically, as long as a CRT is used, it is enough for the lenticular lenses to have a pitch between 0.5 mm and 2.0 mm, but when an LCD or DLP projector, or the like is used, the lenticular lenses are required to have a fine pitch between 0.05 mm and 0.3 mm.
The method described in Japanese Laid-Open Patent Publication No. 120102/1997, for example, has been known as a method of creating light-shielding areas 14a in a light-shielding layer 14 that is used in a fine-pitch lenticular lens sheet 12 of the above-described type. In this method, an ionizing-radiation-curing resin layer is formed on the flat surface of a lenticular lens sheet opposite to the lens-provided surface (the surface on which lenticular lenses are formed), and ultraviolet light is applied to the lenticular lens sheet from the lens-provided surface side to expose the ionizing-radiation-curing resin layer, thereby curing those parts of the resin layer that are in the positions corresponding to the light-converging parts of the lenticular lenses. Making use of the stickiness of the surfaces of those parts of the resin layer other than the cured parts, a toner or transfer ink layer (black in color) is adhered to the surfaces of those parts of the resin layer that are in the positions corresponding to the non-light-converging parts of the lenticular lenses. A light-shielding layer having therein a predetermined light-shielding pattern is thus formed on the lenticular lens sheet on its light-emerging surface side.
However, the lenticular lens sheet produced by the method described in the above publication is at a disadvantage in that the light-shielding pattern in the light-shielding layer is poor in positional accuracy. Another drawback is as follows: the light-shielding effect of the light-shielding layer is insufficient, so that when this lenticular lens sheet is combined with a light-converging lens means such as a Fresnel lens sheet to make a rear projection screen, sufficiently high optical efficiency cannot be obtained, and, in addition, it is highly possible that high image contrast cannot be obtained.
Further, in the method described in the above publication, the process of creating the light-shielding areas requires the step of forming an ionizing-radiation-curing resin layer; the step of curing, by exposure, those parts of the resin layer that are in the positions corresponding to the light-converging parts of the lenticular lenses, leaving the surfaces of the other parts of the resin layer sticky; the step of adhering a toner or transfer ink layer to the non-light-converging parts; and so forth. This method thus requires a large number of steps, so that it is poor in efficiency.
The present invention was accomplished in the light of the aforementioned drawbacks in the background art. An object of the present invention is therefore to provide a lenticular lens sheet that comprises a light-shielding layer having a light-shielding pattern formed with high positional accuracy and that ensures sufficiently high image contrast even when it is combined with a light-converging lens means such as a Fresnel lens sheet to make a rear projection screen, and a process of producing such a lenticular lens sheet.
Another object of the present invention is to provide a lenticular lens sheet for use in a rear projection screen, that comprises a light-shielding layer and that can be produced with higher efficiency, and a process of producing such a lenticular lens sheet.
The main feature of the present invention is that: the light-shielding layer that is formed on the lenticular lens sheet on its light-emerging surface side is made from a silver salt emulsion (a silver salt photosensitive material) which is widely used in the fields of photography and medical service. With the use of a silver salt photosensitive film or the like, a silver salt emulsion layer is laminated to the light-emerging surface of the lenticular lens sheet opposite to its lens-provided surface (the surface on which lenticular lenses are formed). Exposure light is applied to the lenticular lens sheet from its lens-provided surface side to expose the silver salt emulsion layer, and development is then conducted to darken the unexposed parts of the silver salt emulsion layer, whereby a light-shielding layer with a predetermined light-shielding pattern is formed on the lenticular lens sheet on its light-emerging surface side. It is thus possible to obtain the light-shielding pattern of the light-shielding layer with high positional accuracy. Further, it is possible to vary the degree of darkening of the uncured parts according to the rate of exposure of the silver salt emulsion layer or to the degree of development. Therefore, if the optical transmission density of the light-shielding areas in the light-shielding layer is made especially high, there can be obtained a lenticular lens sheet for use in a rear projection screen, having low reflectance for extraneous light, that is, capable of attaining high image contrast.
Specifically, the present invention provides, as a first aspect, a lenticular lens sheet comprising: a light-transmitting lens sheet body having a lenticular lens group consisting of multiple lenticular lenses arranged on one surface; and a light-shielding layer made from a silver salt emulsion, laminated to the other surface of the lenticular lens sheet body; wherein the light-shielding layer has light-transmitting areas in the positions corresponding to the light-converging parts of the lenticular lenses on the lens sheet body, and light-shielding areas that are in the positions corresponding to the non-light-converging parts of the lenticular lenses and that have light-shielding characteristics owing to the darkened silver dispersed in the silver salt emulsion.
In the first aspect of the present invention, the light-shielding areas in the light-shielding layer have an optical transmission density of preferably 2 or more, more preferably 3 or more.
Further, in the first aspect of the present invention, the lens sheet body is preferably a transparent, single-layer sheet with the lenticular lens group integrally shaped.
In the first aspect of the present invention, it is also preferable that the lens sheet body includes a transparent film, and a lenticular lens layer with the lenticular lens group shaped, the lenticular lens layer being laminated to the transparent film.
In the first aspect of the present invention, it is also preferable that the light-shielding layer be laminated to the surface of the lens sheet body opposite to the surface having the lenticular lens group, with a transparent film different from the lens sheet body being disposed between the lens sheet body and the light-shielding layer. The transparent film, to which the light-shielding layer is laminated, may be laminated to the surface of the lens sheet body opposite to the surface having the lenticular lens group with the use of an adhesive agent layer.
In the first aspect of the present invention, it is also preferable that the lenticular lens sheet further comprises a plate-like supporting member capable of transmitting light, the supporting member being laminated to the lens sheet body on the lenticular lens group side or the light-shielding layer side.
In addition, in the first aspect of the present invention, it is preferable that the outermost surface of the lenticular lens sheet on the light-shielding layer side has a reflectance of not more than 10%. Further, it is preferable that the light-shielding areas in the light-shielding layer have, for light of 700 nm, a spectral reflectance 90 to 110% of that for light of 400 nm.
The present invention provides, as a second aspect, a process of producing a lenticular lens sheet, comprising the steps of: preparing a light-transmitting lens sheet body having a lenticular lens group consisting of multiple lenticular lenses arranged on one surface; laminating a silver salt emulsion layer to the other surface of the lenticular lens sheet body; applying exposure light to the lens sheet body from the lenticular lens group side to expose those parts of the silver salt emulsion layer that correspond to the light-converging parts of the lenticular lenses; and developing the silver salt emulsion layer to obtain a light-shielding layer having light-transmitting areas in the positions corresponding to the light-converging parts of the lenticular lenses, and light-shielding areas that are in the positions corresponding to the non-light-converging parts of the lenticular lenses and that have light-shielding characteristics owing to the darkened silver dispersed in the silver salt emulsion.
In the second aspect of the present invention, the silver salt emulsion layer is developed so that the light-shielding areas in the light-shielding layer can have an optical transmission density of preferably 2 or more, more preferably 3 or more.
Further, in the second aspect of the present invention, it is preferable to prepare, for the lens sheet body, a transparent, single-layer sheet with the lenticular lens group integrally shaped.
Furthermore, in the second aspect of the present invention, the process further preferably comprises the steps of: preparing a mold roll for shaping lenticular lenses, whose periphery, serving as a mold face, is provided with grooves in the inverse shape of the lenticular lens group; winding a transparent film around the mold face of the mold roll, with an ionizing-radiation-curing resin composition between the mold face of the mold roll and the transparent film; and applying ionizing radiation to the mold roll through the transparent film to cure the ionizing-radiation-curing resin composition; whereby a sheet including a transparent film, and a lenticular lens layer with the lenticular lens group shaped, the lenticular lens layer being laminated to the transparent film, is prepared for the lens sheet body.
In the second aspect of the present invention, it is preferable that the lamination of the silver salt emulsion layer to the surface of the lens sheet body opposite to the surface having the lenticular lens group be conducted by applying a silver salt emulsion to the former surface of the lens sheet body and drying the silver salt emulsion applied.
In the second aspect of the present invention, it is also preferable that the lamination of the silver salt emulsion layer to the surface of the lens sheet body opposite to the surface having the lenticular lens group be conducted by backing a silver salt emulsion layer with a transparent film to obtain a silver salt photosensitive film and adhering this silver salt photosensitive film to the lens sheet body, with the transparent film of the photosensitive film facing the surface of the lens sheet body opposite to the surface having the lenticular lens group.
In the second aspect of the present invention, it is preferable to use parallel rays for the exposure light. It is herein preferable that the parallel rays have a parallelism of 0xc2x0. It is also preferable that the parallel rays have a parallelism of more than 0xc2x0 and 10xc2x0 or less. A Fresnel printer, or a system composed of a light source and a louver through which light from the source can pass can be used as an exposure system capable of applying the parallel rays.
In the first aspect of the present invention, the light-shielding layer laminated to the surface of the lens sheet body opposite to the surface having the lenticular lens group is formed from a silver salt emulsion, and the light-transmitting areas and the light-shielding areas are created by patterning the light-shielding layer, making use of the difference in the degree of darkening of silver dispersed in the silver salt emulsion. It is therefore possible to make the light-shielding pattern in the light-shielding layer with high positional accuracy. Further, the light-shielding areas in the light-shielding layer can shield light thanks to the darkened silver dispersed in the silver salt emulsion, so that the reflection of extraneous light on the front (viewing plane) side can effectively be suppressed. It is thus possible to obtain sufficiently high image contrast even when the lenticular lens sheet is combined with a light-converging lens means such as a Fresnel lens sheet to make a rear projection screen.
Further, in the first aspect of the present invention, if the optical transmission density of the light-shielding areas in the light-shielding layer is made 2 or more, the light-shielding areas can surely show the light-shielding effect. In addition, since the light-shielding areas in the light-shielding layer have low reflectance, the reflectance for extraneous light on the front (viewing plane) side can be suppressed to low.
Furthermore, in the first aspect of the present invention, if the optical transmission density of the light-shielding areas in the light-shielding layer is made 3 or more, the light-shielding areas can more surely show the light-shielding effect. In addition, since the light-shielding areas in the light-shielding layer have low reflectance, the reflectance for extraneous light on the front (viewing plane) side can be suppressed to lower.
Furthermore, in the first aspect of the present invention, if a transparent, single-layer sheet with a lenticular lens group integrally shaped is prepared for the lens sheet body, it becomes possible to simplify the structure of the lens sheet body.
Furthermore, in the first aspect of the present invention, if a transparent film, to which a lenticular lens layer having the lenticular lens group shaped is laminated, is prepared for the lens sheet body, it becomes possible to make the lens sheet body with high accuracy and efficiency.
Furthermore, in the first aspect of the present invention, since the light-shielding layer made from a silver salt emulsion may be laminated to the lens sheet body with a transparent film different from the lens sheet body being disposed between the lens sheet body and the light-shielding layer, a silver salt photosensitive film such as a conventional photographic silver salt film can be used to form the light-shielding layer.
Furthermore, in the first aspect of the present invention, since the transparent film, to which the light-shielding layer is laminated, may be laminated to the lens sheet body with the use of an adhesive agent layer, a silver salt photosensitive film such as a conventional photographic silver salt film can be used to form the light-shielding layer and can thus be readily fixed to the lens sheet body.
Furthermore, in the first aspect of the present invention, if the lenticular lens sheet further comprises a light-transmitting, plate-like supporting member laminated to the lens sheet body on its lenticular lens group side or the light-shielding layer side, it becomes self-supporting and can well maintain its shape even when it is in the standing state.
Furthermore, in the first aspect of the present invention, if the outermost surface of the lenticular lens sheet on its light-shielding layer side is made to have a reflectance of not more than 10%, the lowering of image contrast that is caused by extraneous light can be suppressed to extremely small.
Furthermore, in the first aspect of the present invention, if the light-shielding areas in the light-shielding layer are made to have, for light of 700 nm, a spectral reflectance 90 to 110% of that for light of 400 nm, they are seen black or nearly black and thus have lowered visual sensitivity. It is therefore possible to effectively prevent the lowering of image contrast that is caused by extraneous light.
According to the second aspect of the present invention, the light-shielding layer having a predetermined light-shielding pattern is formed on the lens sheet body on its light-emerging surface side in the following manner: a silver salt emulsion layer is laminated to the surface of the lens sheet body opposite to the surface having the lenticular lens group; exposure light is applied to the lens sheet body from the lenticular lens group side to expose the silver salt emulsion layer; and the silver salt emulsion layer is then developed to darken its unexposed parts. It is therefore possible to produce a lenticular lens sheet comprising the light-shielding layer with higher efficiency. It is also possible to form the light-shielding pattern in the light-shielding layer with high positional accuracy. In addition, the light-shielding areas in the light-shielding layer can shield light thanks to the darkened silver dispersed in the silver salt emulsion, so that it is possible to effectively suppress the reflection of extraneous light on the front (viewing plane) side. Sufficiently high image contrast can thus be obtained even when the lenticular lens sheet is combined with a light-converging lens means such as a Fresnel lens sheet to make a rear projection screen.
In the second aspect of the present invention, if the silver salt emulsion layer is developed so that the light-shielding areas in the light-shielding layer can have an optical transmission density of 2 or more, the light-shielding areas can surely show the light-shielding effect. In addition, since the light-shielding areas in the light-shielding layer have low reflectance, the reflectance for extraneous light on the front (viewing plane) side can be suppressed to low.
Furthermore, in the second aspect of the present invention, if the silver salt emulsion layer is developed so that the light-shielding areas in the light-shielding layer can have an optical transmission density of 3 or more, the light-shielding areas can more surely show the light-shielding effect. In addition, since the light-shielding areas in the light-shielding layer have low reflectance, the reflectance for extraneous light on the front (viewing plane) side can be suppressed to lower.
Furthermore, in the second aspect of the present invention, if a transparent, single-layer sheet with the lenticular lens group integrally shaped is prepared for the lens sheet body, it becomes possible to simplify the structure of the lens sheet body.
Furthermore, in the second aspect of the present invention, if a transparent film, to which a lenticular lens layer made from an ionizing-radiation-curing composition is laminated, is prepared for the lens sheet body by the use of a mold roll for shaping lenticular lenses, whose periphery, serving as a mold face, is provided with grooves in the inverse shape of the lenticular lens group, it becomes possible to make the lens sheet body with high accuracy and efficiency.
Furthermore, in the second aspect of the present invention, if the lamination of the silver salt emulsion layer to the lens sheet body is conducted by applying a silver salt emulsion to the lens sheet body, and drying the silver salt emulsion layer applied, it becomes possible to make the lamination structure of the finally obtained lenticular lens sheet simple.
Furthermore, in the second aspect of the present invention, if the lamination of the silver salt emulsion layer to the lens sheet body is conducted by adhering a silver salt photosensitive film prepared by backing a silver salt emulsion layer with a transparent film, it is possible to form the silver salt emulsion layer with higher accuracy.
Furthermore, in the second aspect of the present invention, if parallel rays are used for the exposure light, the light-shielding areas can be accurately created in the light-shielding layer centered on the non-light-converging parts of the lenticular lenses.
Furthermore, in the second aspect of the present invention, if the parallelism of the parallel rays is made 0xc2x0, it is possible to accurately create, in the light-shielding layer, the light-shielding areas with a preferable width.
Furthermore, in the second aspect of the present invention, if the parallelism of the parallel rays is made more than 0xc2x0 and 10xc2x0 or less, it is possible to create, in the light-shielding layer, the light-shielding areas with the desired width.
Furthermore, in the second aspect of the present invention, if a Fresnel printer is used as an exposure system capable of applying the parallel rays, it is possible to maintain the flatness of the lenticular lens sheet during exposure and thus to attain improved exposure accuracy.
Furthermore, in the second aspect of the present invention, if a system composed of a light source and a louver through which light from the light source can pass is used as an exposure system capable of applying the parallel rays, it is possible to conduct exposure while easily controlling the parallelism of the parallel rays.